1. Field of the Invention
The present invention relates to improvements in a wire electrical discharge machine for supplying electricity to a wire electrode traveling in an upper or lower wire guide section.
2. Description of the Related Art
A conventional wire electrical discharge machine will be described with reference to FIGS. 6 and 7. In FIGS. 6 and 7, the wire electrical discharge machine is comprised of a bed 1 serving as a base; a table 5 for fixing a workpiece 3 which is processed by a wire electrode 2; a processing tank 7 in which a working fluid is stored; an X-axis driving section 13 for moving the table 5 in an X-axis direction by moving an X-axis table 9 by driving an X-axis motor 8; a Y-axis driving section 17 for moving the table 5 in a Y-axis direction by causing a column 19 to move along a longitudinal direction of a lower arm 20 fixed to the base 1, by driving a Y-axis motor 15; a Z-axis driving section 21 for moving the table 5 in a Z-axis direction and fixed to the column 19; a lower wire guide 25 fixed to the lower arm 20 via an insulating plate on a vertical surface of a distal end of the lower arm 20; an upper wire guide 30 fixed to a distal end portion of the Z-axis driving section 21 so as to guide the wire electrode 2; an electric supply section 60 incorporated in the upper wire guide 30 so as to supply electricity to the wire electrode 2; and a feeding/collecting section for feeding and collecting the wire electrode 2.
The upper wire guide 30 allows the working fluid to flow to the workpiece 3 while guiding the wire electrode 2, and is arranged such that an upper end portion of a guide body portion 33 having a collar is engaged with and fixed to a guide attaching plate 31 which has a channel for supplying the working fluid to the workpiece 3 and a guide hole for passing the wire electrode 2 therethrough. A hollow cylindrical portion for guiding the wire electrode 2 is provided in the guide body portion 33. In this cylindrical portion, a cooling hole 33x for allowing the working fluid for cooling the wire electrode to flow in its interior is provided, and as a central hole of a rectifying plate 35 having a plurality of holes 35a for the working fluid to flow therethrough is engaged with and fixed to an outer peripheral surface of the cylindrical portion, a pool 36 is formed between a channel outlet of the guide attaching plate 31 and the holes 35a of the rectifying plate 35.
A lower auxiliary guide 38 for guiding the wire electrode 2 is fixed in the interior of a lower portion of the guide body portion 33, and an upper auxiliary guide 39 is also fixed in the interior of an auxiliary plate 37 fixed to an upper portion of the guide attaching plate 31. It should be noted that the guide attaching plate 31 and the auxiliary plate 39 are fixed to an upper block 41.
A jet nozzle 40 for guiding the wire electrode 2 into a guide hole in the lower wire guide 25 by means of the fluid has its outer peripheral surface fixed to an inner peripheral surface of the rectifying plate 35, and has a collar whose top surface is fixed to a holding portion 35b of the rectifying plate 35 via a spring 45, the jet nozzle 40 and the like being covered with a working fluid nozzle 47. The arrangement provided is such that the tip of the jet nozzle 40 returns to avoid contact with the workpiece 3 as the spring 45 is compressed by the pressure of the fluid to lower the tip of the jet nozzle 40 and stop the supply of the working fluid. It should be noted that a pipe 50 for the jet nozzle 40 and a pipe 55 for the working fluid nozzle 47 are connected to inlet ports of the guide attaching plate 31. In addition, since the basic configuration of the lower wire guide is identical to that of the upper wire guide, a description thereof will be omitted.
The electric supply section 60 is comprised of an electric supply die 62 for supplying electricity to the wire electrode 2, a die holding plate 64 for fixing this electric supply die 62 and pressing it toward the wire electrode 2 side, and a drawer plate 66 capable of inserting or withdrawing the electric supply die 62, the electric supply die 62 being electrically connected to an unillustrated power source.
The wire electrode feeding/collecting section is arranged such that the wire electrode 2 passes through a pipe 89 and is accommodated in a collecting box 90 by means of rollers 83, 85, and 87 for changing the direction of the wire electrode 2 wound around a wire bobbin 80.
Referring to FIGS. 6 and 7, a description will be given of the operation of the wire electrical discharge machine having the above-described construction. First, when the working fluid is supplied to the pipe 50, the jet nozzle 40 moves downward under the pressure of the working fluid while pressing the spring 45, and a jet stream jets out from a jetting hole 40a of the jet nozzle 40, which in turn causes the wire electrode 2 to pass through the interior of this jet stream and guides the wire electrode 2 to the lower wire guide 25, connecting the wire electrode 2 thereto.
During processing, the working fluid from the pipe 50 is stopped, which in turn causes the jet nozzle 40 to return upward by means of the spring 45, and the working fluid from the pipe 55 passes through the channel inside the guide attaching plate 31, the curving and the like of the fluid due to the occurrence of turbulence being alleviated by means of the pool 36. The working fluid then passes through the holes 35a in the rectifying plate 35 for stabilizing the direction in which the working fluid jets out from a jetting hole 47a of the working fluid nozzle 47, and the working fluid jets out from the jetting hole 47a.
Meanwhile, the wire electrode 2 is energized by the unillustrated power source through the electric supply die 62. At the same time, since a large current flows across the contacting portions of the electric supply die 62 and the wire electrode 2, and intense heat is produced therein, the working fluid is supplied from the cooling hole 33x to a wire passage 31a by being raised upward by means of the back pressure inside the working fluid nozzle 47, and passes the contacting portions, thereby absorbing Joule heat produced in the contacting portions. Accordingly, processing is continued while maintaining the contacting portions at a substantially fixed temperature. It should be noted that the electric supply die in the lower guide is also cooled by similar action.
Electrical discharge between the workpiece 3 and the wire electrode 2 is continued, and while the table 5 is being moved along the X-, Y-, and Z-axes by moving the X-axis driving section 17, the Y-axis driving section 19, and the Z-axis driving section 21, the high-speed working fluid from the working fluid nozzle 47 is supplied to a gap between the workpiece 3 and the working fluid nozzle 47 (hereafter referred to as the gap between the electrodes), thereby discharging and removing the processing sludge produced in the gap between the electrodes. While electrical discharge is continued in a state in which a proper gap is maintained between the electrodes and the resistance value is maintained to a fixed value, processing is continued.
However, with the electrical discharge machine having the above-described construction, as the wire electrode 2 travels while vibrating at its portion of contact with the electric supply die 62, noncontacting portions are produced and very small arc discharge occurs at the noncontacting portions. Accordingly, the surface of the electric supply die 62 becomes roughened, and the wire electrode 2 which is softer than the electric supply die 62 becomes eroded, thereby producing wire dust. Moreover, also in the electric supply die of the lower wire guide, the surface of the electric supply die which passed after machining becomes roughened due to discharge craters, exhibiting the aforementioned action more noticeably. As a means for preventing such a phenomenon, it is conceivable to move the position of the electric supply die 62 forward with respect to the wire electrode 2 so as to enlarge the frictional resistance due to contact with the wire electrode 2. However, there is a problem in that mechanical contact wear increases, and the wire electrode 2 is more liable to be eroded.
In the cooling of the electric supply die 62, the working fluid is supplied from the cooling hole 33x to the contacting portions by means of the back pressure of the interior of the nozzle. However, if the working nozzle and the workpiece become spaced apart from each other, the back pressure cannot be obtained sufficiently, making it impossible to supply the working fluid sufficiently to the contacting surface of the electric supply die 62. In particular, if the working current becomes large, the Joule heat at the contact energizing portion becomes large. Hence, the temperature rise increases, the wire electrode 2 is eroded, so that an irregular surface is produced on the surface, and a large quantity of dust is produced. Therefore, the wire electrode 2 possibly becomes disconnected when it vibrates at the irregular surface, the supply of current becomes unstable, and the passage of the wire electrode 2 becomes loaded with the dust. For this reason, there has been a problem in that machining must be effected by lowering the machining speed of the workpiece 3.